Well, it’s a high-fat, low-carb, moderate-protein diet that was originally conceived for patients with seizure disorders. Its goal is to get you to a metabolic state called ketosis, in which the body’s cells burn fragments of fats called ketones instead of glucose for fuel. It’s touted for weight loss because it causes the body to use stored fat for fuel instead of carbs—but it’s not sustainable because eventually you’ll want to eat stuff like potatoes and bread. In other words: Try another diet.